The present invention relates to a mounting structure for a sensor in an industrial vehicle such as a forklift.
A typical industrial vehicle such as a forklift has various sensors including a yaw rate sensor for detecting the state of the vehicle. The detection values of the sensors are used in various controls for optimizing the state of the vehicle. The sensors must be located in the body frame.
Some forklifts are used in environments of extreme temperatures such as in a factory having a furnace or in a refrigerator. In other words, the sensors in the body frame are also used in extreme temperatures.
For example, a yaw rate sensor has a temperature range in which the sensor functions properly. If the temperature of the sensor is out of the range, the sensor may fail to function properly. Even if the sensor temperature remains in the range, a significant temperature change of the sensor alters the sensitivity of the sensor, which changes the detection accuracy. Further, some yaw rate sensors are not waterproof and fail to function when rain or wash water is splashed on the sensor.
Accordingly, a sensor like a yaw rate sensor needs to be located such that the sensor is not excessively heated by engine heat and ambient heat. Also, a sensor must be prevented from getting wet with rain and wash water.
Vibrations generated in the body frame of a vehicle are transmitted to sensors in the body frame. Some sensors such as a yaw rate sensors are easily damaged by vibrations.
To prevent vibrations from being transmitted to sensors, some sensors are supported by rubber cushions. The cushions dampen vibrations from the body frame to the sensors thereby preventing violent vibrations from being transmitted to the sensors. The sensors are therefore less vulnerable to damage.
However, the degree of vibration damping depends on the frequency of vibrations generated in the body frame. The natural frequency of a vibrating system, which includes a rubber cushion and a sensor, is determined by the spring constant of the rubber cushion and the weight of the sensor. A frequency range lower than the natural frequency is referred to as a resonance region and a frequency range higher than the natural frequency is referred to as a damping region. If the vibration of the body frame is in the damping range, the rubber cushion damps the vibration from the body frame. If the vibration of the body frame is in the resonance region, the vibration in the sensor is stronger than the vibration of the body frame.
Every sensor has its own natural frequency. If the frequency of vibration from the body frame matches the natural frequency of the sensor, a strong resonance is generated in the sensor. The natural frequency of a sensor is relatively low and is sometimes in the resonance region of a vibrating system. In this case, the yaw rate sensor can be strongly vibrated when the vehicle is moving.
During assembly of a vehicle, bolts are often fastened with an impact wrench. A sensor may be fastened to the body frame with an impact wrench. The frequency of the vibrations transmitted from the impact wrench to the body frame is relatively low and is in the resonance region of the vibrating system using a rubber cushion. Thus, the vibration from the impact wrench cannot be damped by the rubber cushion. Therefore, when attaching a fragile sensor such as a yaw rate sensor to a body frame, the sensor may be broken by the impact wrench vibrations.
Further, if low frequency vibrations are generated in the body frame, the vibrations can cause resonance in a yaw rate sensor. This affects the detection accuracy of the yaw rate sensor. In other words, the yaw rates detected by the sensor may be erroneous.
Accordingly, it is a first objective of the present invention to provide a sensor mounting structure that permits the sensor to function accurately by preventing the temperature of the sensor from excessively increasing or decreasing due to engine heat and the ambient temperature and by preventing the sensor from becoming wet.
A further objective of the present invention is to provide an industrial vehicle that improves the accuracy of controls performed based on detection values of sensors mounted on the vehicle body frame.
A further objective of the present invention is to provide a sensor mounting structure for vehicles that protects the sensor from vibration transmitted from the body frame of a vehicle.
A further objective of the present invention is to provide a sensor mounting structure for vehicles that protects the sensor from vibrations having the same frequency as the natural frequency of the sensor.
Another objective of the present invention is to provide a sensor mounting structure for vehicles that protects the sensor from vibrations transmitted to a body frame from an impact wrench when the sensor is being installed in the body frame.
Another objective of the present invention is to provide a sensor mounting structure for vehicles that reduces detection errors of a yaw rate sensor that is supported on a body frame by a vibration damping member.
A further objective of the present invention is to provide a vehicle that improves the reliability of controls performed based on detection values of sensors supported on a body frame.